[spoiler]Why the answer is B not A?[/spoiler]

B tells us that the species(?) shed their tail when attacked by the predator, if this is true, then the fossil remains would not have tail at all, since the species might have encountered at least 1 predator in its life cycle. I hope I am clear. Still mushy though...

Hi hemant_rajput, What is the source of this CR prompt? I only ask because it doesn't follow the typical GMAT "style" for this type of question. Normally, this type of question is framed with the word EXCEPT (e.g. "Each of the following is a reasonable explanation EXCEPT"). In these prompts, the four answers fit the situation while the "exception" does not. Each of the 5 answers here has enough logic in it to be considered a potential explanation. However, here's what I think the "intent" of the question is: Answers A, C, D and E give us a logical factoid that would explain the difference in tail size. Answer B gives us a theory of something that might have happened (but maybe didn't) and if it happened at all, it only happened sometimes. That's not a great piece of evidence, so the author of this prompt probably considered it the correct answer. The real GMAT won't be this "thin" with the logic in a CR question. GMAT assassins aren't born, they're made, Rich

I am confused as well - My reasons - a> May be in 2 million years of evolution changed the length of the tail but not sure (Contender) b> May be one of them encountered a predator and the other one didn't (helps - ruled out) c> Younger one has smaller tail and the adult has longer one (helps - ruled out) d> Length can be different because of difference in gender (helps - ruled out) e> food supply impacts the difference in length. No information to suggest that the fossils were from same age (contender)